The present invention relates to primerless silicone hardcoat compositions comprising an aqueous/organic solvent silicone dispersion consisting essentially of colloidal silica, and a partial condensate of an organoalkoxysilane, in combination with an effective amount of an adhesion promoter in the form of a caprolactone based polyester polyol.
Prior to the present invention, as shown by Patel, U.S. Pat. No. 5,041,313, silicone hardcoat composites were made by initially priming a thermoplastic substrate, such as a polycarbonate substrate, with a solution of a polyacrylic resin in a solvent blend, followed by the application of a silicone hardcoat composition. European patent application 0439294A1 suggests that priming a thermoplastic substrate prior to the application of the silicone hardcoat is not necessary if a monomeric hydroxy acrylate such as 2-hydroxy ethyl methacrylate is added to the hardcoat mixture before it is thermally cured. However, the use of hydroxy acrylates in coating compositions has sometimes been restricted because of their toxicity, as taught in Chung, U.S. Pat. No. 4,486,504.
In copending application Ser. No. 07/880,777, filed May 11, 1992, now pending it was found that an acrylated or methacrylated polyurethane, or an acrylic polyol copolymer, having an M.sub.n (number average molecular weight) of at least 1000 could be used as an adhesion promoter in the aqueous/organic solvent silicone dispersion. The term "aqueous/organic solvent silicone dispersion" means a dispersion consisting essentially of colloidal silica and the partial condensate of an organoalkoxysilane as defined in more detail hereinafter. The resulting silicone hardcoat compositions can be applied directly onto a variety of unprimed thermoplastic substrates, such as a polycarbonate substrate, followed by a thermal cure to provide thermoplastic composites exhibiting improved adhesion and weathering resistance.